Pulverizing mills are used in a variety of applications to reduce particle size in wet or dry foodstuffs, chemicals, plastics and pharmaceutical materials. Such machines typically are constructed as hammer mills, with the feed material being introduced through an inlet housing to a chamber where the pulverizing or communiting is accomplished, and with the pulverized material discharging through a screened opening into a suitable receptacle. Such prior art machines are typically illustrated in the following U.S. patents:
Magnus U.S. Pat. No. 2,348,916 (May 16, 1944)
Gruendler U.S. Pat. No. 2,969,820 (Jan. 31, 1961)
Kircher, Jr. U.S. Pat. No. 3,051,400 (Aug. 28, 1962)
Joseph, et al U.S. Pat. No. 3,088,683 (May 7, 1963)
Fitz U.S. Pat. No. 3,184,172 (May 18, 1965)
MacElvain, et al U.S. Pat. No. 4,098,466 (July 4, 1978)
Mills of the sort typified by the foregoing prior art patents are not always suitable for certain kinds of foodstuff and pharmaceutical processing for several reasons.
First, there exist strict rules with respect to cleanliness and sanitation for equipment used in food and drug processing. For example, Title 21 C.F.R. section 110.40(a) (1984) requires all plant equipment and utensils used in processing food for human consumption to be so designed and of such material and workmanship as to be adequately cleanable, and to be so installed and maintained as to facilitate the cleaning of the equipment and of all adjacent spaces. Devices such as those shown in the above patents typically contain multiple moving parts such as swinging arms, blades and the like, with numerous pivots, joints and crevices which tend to catch and retain particles of material.
Second, it is often important to prevent excessive buildup of heat in the product as it passes through the mill, in order to avoid adverse physical and chemical changes. This requirement cannot always be met with a mill that depends on multiple recirculation of the material through the mill, as opposed to substantially once-through processing where the majority of the material is reduced to the desired size in just one pass.
Third, it is desirable to be able to use the same mill for different products without the need to disassemble the entire unit for the purpose of changing impact bars or blades.
Finally, safety considerations often require that the mill's power source be positively locked out when the mill is open for cleaning or other maintenance. At the same time it is often desirable to reverse the direction of mill rotation to utilize the opposite face of the rotor, which may have a different contour. This requires that the inlet housing be repositioned in the opposite direction to prevent blow-back of product through the inlet opening, and care must be taken in insure that the mill is not inadvertently driven in the wrong direction after reassembly.
In view of the foregoing considerations, it is a principal object of the present invention to provide an improved impact or pulverizing mill which has a unitary and substantially crevice-free rotor which is easily cleanable and requires little or no disassembly or maintenance.
It is a further object of the invention to provide such a mill which is capable of using different blade lengths, but which is still capable of relatively high speed operation with substantially once-through passage of feed material, so as to avoid unnecessary heat build-up in the product.
Another object and feature of the invention is to provide a mill which is quickly and easily opened for cleaning and maintenance, and which is provided with safety interlocks to prevent the mill from being accidentally started if the inlet housing is not positively secured in proper position for operation.
A related object of the invention is to provide for reversible rotation of the mill by merely removing and repositioning the inlet housing, and to provide for the direction of operation to be automatically determined upon reassemble of the inlet housing in the desired position.